On Fri, 6 Jul 2007, Heikki Linnakangas wrote:
> There's something wrong with that. The number of buffer allocations shouldn't
> depend on the bgwriter strategy at all.
I was seeing a smaller (closer to 5%) increase in buffer allocations
switching from no background writer to using the stock one before I did
any code tinkering, so it didn't strike me as odd. I believe it's related
to the TPS numbers. When there are more transactions being executed per
unit time, it's more likely the useful blocks will stay in memory because
their usage_count is getting tickled faster, and therefore there's less of
the most useful blocks being swapped out only to be re-allocated again
later.
Since the bad bgwriter tunings reduce TPS, I believe that's the mechanism
by which there are more allocations needed. I'll try to keep an eye on
this now that you've brought it up.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD